"T-bag" reffers to the scrotum. "T-bagging" oringanally meant putting ones scrotum into someones mouth while they are asleep. The term "T-bagging" is popular from the game "Halo" and it refers to a movement that the character makes by kneeling down over the head of a dead opponent.

John: Haha! Take that t-bag!

Anthony: *mumbles* it wont be so funny when i t-bag you in your sleep.

The Urban Dictionary T-Shirt

Theodore "T-Bag" Bagwell is a character on Prison Break played by Robert Knepper. Incarcerated for 40 counts of kidnapping, rape and murder, T-Bag is held at Fox River Prison in Chicago.
He is loved for his dark side and witty sense of humour

Example 1:T-Bag: What's that smell? Smells like....conspiracy
Example 2:T-Bag: Did I say you could talk cherry? You'll know when I want you to open your mouth.

The Urban Dictionary T-Shirt

Typical Bay Area Guy, also see douchebag, refers to the strange phenomenon occurring in the Bay area over the last 15 years that has resulted in the majority of the women all competing over the tiny population of "desirable" guys. A man who, in any other major city might be considered average, is now considered a "hot commodity". Despite the fact that there are more men in the population, most are either gay, taken, undesirable or don't speak English. This allows the TBAGs to develop sever commitment issues and act like they are God's gift. Most Bay Area women who spend years of frustration in the dating scene, notice an immediate shift in their love life if they are lucky enough to move out of the area. TBAGs typically range in the 21-45 category, or until they start to get bald and fat.

Tina dated a TBAG who after 7 years, still didn't refer to her as his girlfriend.

The Urban Dictionary T-Shirt

A brother with the name Travis that is a complete loser. That spoils or ruins an otherwise enjoyable event, esp. when in relation to ruining a drunken stooper. So there for you just want to punch him right in his nut bags.